regulator: ltc3589: Make IRQ optional

It's perfectly valid to use the LTC3589 without an interrupt pin
connected to it. Currently, the driver probing fails when client->irq
is 0 (which means "no interrupt"). Don't register the interrupt
handler in that case but successfully finish the device probing instead.
Signed-off-by: Bernhard Walle <bernhard@bwalle.de>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/ltc3589.c

@@ -520,13 +520,16 @@ static int ltc3589_probe(struct i2c_client *client,
 		}
 	}
 
-	ret = devm_request_threaded_irq(dev, client->irq, NULL, ltc3589_isr,
+	if (client->irq) {
+		ret = devm_request_threaded_irq(dev, client->irq, NULL,
+						ltc3589_isr,
 						IRQF_TRIGGER_LOW | IRQF_ONESHOT,
 						client->name, ltc3589);
 		if (ret) {
 			dev_err(dev, "Failed to request IRQ: %d\n", ret);
 			return ret;
 		}
+	}
 
 	return 0;
 }